Integrated optical switches have been widely used recently. To divert light from one waveguide to another, the waveguides are coupled by specific geometric arrangements of the two waveguides in relation to each other, where the coupling is modified by local electro-optical manipulation of their indices of refraction. Typical examples of electro-optical switches include the Mach-Zehnder interferometer 2×2 switch, the directional coupler 2×2 switch, the modal-interference 2×2 switch (e.g., two-mode interference switch, bifurcation optical active switch), the mode-evolution 2×2 switch, the imbalanced y-branch 1×2 switch, the digital-optical switch, and the total internal reflection (TIR) X-switch. Depending on the voltage applied to such switches or in some cases the electrical current actually, light is thus partly or completely diverted from an input waveguide to an output waveguide.
By appropriately combining waveguides and switches, a switch array (also referred to as switch matrix) is formed to switch light from multiple input waveguides among multiple output waveguides. A variety of switch array geometries have been used. Switch arrays based on geometries such as crossbar geometry can be used to divert input signals to output channels arbitrarily. Signals from any input channels can be directed to any output channel, and even to multiple output channels, in broadcast and multicast transmission modes.
FIG. 1A is a layout illustrating a typical switch array having crossbar geometry. A set of input waveguides 101 crosses a set of output waveguides 102 via multiple switching nodes, such as switching node 103, disposed at the crossing points to divert an incoming optical signal from any one of the input waveguides 101 to any one of the output waveguides 102. FIG. 1B is an enlarged portion of switching node 103 shown in FIG. 1A. Referring to FIG. 1B, an incoming optical signal traveling along waveguide 104 is routed or diverted to one of waveguides 105 and 106 via the switching element 110. The switching element 110 may be referred to herein as an X switch having two input ports and two output ports.
Single crossbar switching elements are used in the structures shown in FIGS. 1A and 1B. Alternatively, a double crossbar switching node may also be used in place of switching node 103. FIG. 2A is a layout illustrating a typical double crossbar switching node. The double crossbar switching node 200 includes switches 203 and 204, which are Y switches. In order to reach from waveguide 201 to waveguide 202, the incoming optical signal is routed by switch 204 onto an intermediate waveguide 205 and routed again by switch 203 onto waveguide 202. In addition, an optical mirror may be used to direct an optical signal from one direction into another direction. FIG. 2B is a layout illustrating a typical optical mirror. The optical mirror 253 is used to direct an incoming optical signal traveling waveguide 251 from one direction to waveguide 252 of different direction.
A typical switch employs the thermo-optic effect in a localized manner to control the refractive index within polymer waveguide structures to switch and attenuate the optical signals, which may limit the switching speed of the switch. Further, there has been a lack of commercially available switches possessing microsecond operation that have integrated variable optical attenuators and integrated optical power monitoring. The lack of integrated power monitoring means external components are required, which makes the overall approach more cumbersome and bulky.